[FEATURE] Map ingested responses to specific users

[burtenshaw]

Is your feature request related to a problem? Please describe.

When ingesting records, the IngestedRecordMapper class assigns all responses to a given user_id. This compromises the portability of datasets.

This also impacts the from_hub method because responses can only be assigned to known users.

Describe the solution you'd like

It would be ideal if users could map the responses to specific users with the mapping parameter.

Describe alternatives you've considered

Currently, we drop responses from unknown users.

Additional context

https://github.com/argilla-io/argilla/pull/5161